What is ISO, exactly?

This useful control allows you to carry on taking pictures when the light level drops

Surprisingly, ISO isn’t a complex technical acronym. While it’s true that it represents the ‘International Organisation for Standardisation’ – the governing body that standardises sensitivity ratings for camera sensors – that would work out as ‘IOS’. No, in fact ‘ISO’ is taken from the Greek word ‘isos’, which means ‘equal’. So we should all be pronouncing it ‘iso’ rather than ‘I-S-O’!

Like aperture and shutter speed, the ISO is measured in stops, which allows you to balance the exposure. Each time it is increased by one stop (brighter), the shutter speed can be made one stop faster (darker) or the aperture can become one stop smaller (darker). Reduce the ISO by one stop, and either the shutter speed can be extended by one stop or the aperture can opened by one stop.

A shot in the dark

Higher ISOs amplify the signal more, allowing you to record images in low light.

Of course, you can still record a picture in low light using a low ISO setting, but you’ll have to use a large aperture to let more light in, or use a slow shutter speed to expose the sensor for longer. Neither of these may be an option.