ISO 101: everything you wanted to know (but were afraid to ask)

What is ISO?

Along with aperture and shutter speed, ISO is one of the main camera settings, and adjusting it will change how your pictures look. ISO affects how sensitive your camera is to light. A low ISO is less sensitive, and a high ISO is more sensitive - so you'd use a high ISO in dimly lit situations.

What does ISO stand for?

A lot of people think that ISO stands for International Standardisation Organisation: the team behind setting standards across manufacturing, engineering and so on, ensuring that products and services are as you'd expect to find them. It means that ISO 100 on a Canon camera will give roughly the same effect as ISO 100 on a Nikon camera. Neat, eh?

Unfortunately for everyone, that organisation doesn't exist: the team who set standards is actually called the International Organisation (for) Standardisation - or IOS. That means ISO's not an acronym. So, what does it mean?

The company's website states that because IOS would read differently in different languages - such as organisation internationale de normalisation in French, which would be OIN - the founders decided to give themselves the short name of ISO. This is derived from the Greek word isos, meaning equal.

How do I pronounce ISO?

Good question. You might hear people saying EYE-ESS-OH - spelling out all the letters - and you'll also hear people pronouncing it EYE-SO. Some people dodge the issue entirely and refer to it as “sensitivity”. We'd go for EYE-SO: think of all the time you save with that missing syllable...

What does changing the ISO do?

Back in pre-digital days, if you wanted to "change the ISO", you had to wait until your film ran out and swap to a different sensitivity film - but now you can switch with the push of a button.

Changing the ISO makes your camera's sensor more sensitive to light. You can try it yourself. Grab your camera, and head somewhere that's a bit dim - inside at dusk should do it. Keep the shutter speed and the aperture the same, and adjust the ISO setting. If you take a picture at ISO 100, it'll be fairly dark and you won't be able to see much in the way of detail - but if you dial up the ISO to its highest setting, you'll be able to pick out much finer points and objects. Take a look at this video and you'll see what we mean!

Changing the ISO also enables you to use a faster shutter speed and a smaller aperture, so you have more creative flexibility and can make a picture look the way you want to. It makes sense: if your sensor's more sensitive/ more able to pick up light, you don't have to leave the camera's shutter open as long. You just might have to deal with a bit of noise in your pictures.

What do people mean when they mention "noise" when talking about ISO?

Noise or grain can be seen as speckled patches in areas of single colour or in shadowy parts of your photos: you'll see more noise if you use higher ISOs, particularly if you're shooting on a camera with a small sensor like a compact or a mobile phone. Smaller sensors and higher ISOs will both tend to increase noise in your pictures, though modern cameras are much better at handling this. The real question is, how much noise is too much noise?

How much noise is too much noise?

That's a personal question and depends on the picture you're taking. If it's a fine, delicate, detailed shot of a single flower, you might find noise distracting - but if you're shooting an action packed shot of football in a floodlit stadium, some noise can add drama and grit to your image. You can also turn an image black & white to make noise turn into a grainy, artistic effect. It's up to you: experiment to find out what you prefer!