Photography ISO

Using ISO on your camera to calculate a change in photography exposure.

ISO stands for International Standards Organisation, a governing body based in Europe that provides standards for a large variety of subjects. The initials are used for film speed or camera speed in photography which rates light sensitivity. In the past it was known as ASA.

Most good digital cameras have an interchangeable ISO rating system. A camera with an ISO setting of 100 is twice as light sensitive as a camera with an ISO of 50. The faster the film, the more sensitive it is to light. If you are taking a low light image with a digital camera use a slow ISO rating of 200 or upwards.

Most digital cameras have changeable ISO settings which should be used according to different types of photography. If you are shooting on a bright day a fast speed or low setting of ISO 50 or ISO 100 should do. On low light scenes an ISO of 400 or higher my be a better choice.

This is the same for photographic film you buy. Each film has an ISO rating and work with the same principles as your digital camera. A film speed of 400 is twice as fast as a film speed of 200, which means that it allows twice the amount of light.

Also note that if you use a high ISO number your image may appear to have noise. Noise will give your images a grain affect when enlarged. All photographers like to have noise free images so selective use of ISO is important.

If you are unsure which setting to use you should keep your camera set on ISO 100. With this setting you will have a good colourful image.

ISO settings can also be important when calculating exposure. As you know, the aperture and shutter in your camera control the amount of light entering you camera. The ISO of your camera or film will also help to calculate tricky exposures.

Lets explain using this example.

You are at a scene and you want to use an exposure of f/22 with the shutter set at 1/2 second and your camera is set at an ISO of 100. The scene you are about to shoot will give you a good shot but there is moving water in the scene and you want to give a steamy effect to the water.

A shutter speed of 1 second will do this but if you keep the aperture set at f/22 you will overexpose the shot. The easiest thing is to set the ISO of your camera to 50.

A setting of ISO 50, and f/22 at 1 second is the same as a setting of ISO 100, and f/22 at 1/2 a second. If you are shooting with a film camera you will need to change the film to ISO 50.

As mentioned earlier, a photography setting of ISO 100 is satisfactory for portraits, landscape and wildlife. Just remember if you are shooting on a very bright day change it to ISO 50 and on a dull day change it to ISO 200.


TJ Tierney is an award winning photographer and a freelance writer. To find out more information visit his photography site and photography forum His site also contains a free photography directory.