ISO

In the ‘olden days’ of film cameras the ISO rating referred to the speed of the film. Obviously digital cameras don’t have film so the ISO now refers to the sensitivity of the image sensor.

The ISO options on my camera range from 100 to 1600 - the lower the number the finer the grain in the photograph and the less sensitive the camera is to light.

If you’re taking pictures in an overly bright situation - such as on a ski slope or the beach on a sunny day you should choose a low ISO setting. If its a cloudy day or you are are shooting pictures indoors then increasing the ISO setting will increase the light sensitivity of the sensor. As the amount of light decreases the camera will slow down the shutter speed to try and let more light in - this can lead to motion blur. Increasing the ISO setting will counteract this and allow for a faster shutter speed.

High ISO settings are also good when you are trying to shoot fast moving people/objects as it allows the camera to gather more light and therefore increases the shutter speed.

The downside of high ISO settings is that the photograph becomes more grainy - this is why you shouldn’t leave your camera on a high ISO setting all of the time.

Every ISO setting has a purpose

Here’s a quick guide as to when you should use each ISO setting:

ISO 100: Perfect for bright sunny days, at the beach or on the snow. Produces clean images that are great for enlargements.

ISO 200: Use on overcast days - some grain may appear but shouldn’t be too noticeable.

ISO 400: Use for lower lighting conditions (indoors, night time) or when shooting faster moving subjects in lower lighting conditions. ISO 400 can make photos look very noisy in dark areas of the picture.

In practice

To test this out I placed Tigger in the bay window on a slightly cloudy day. I fixed the aperture and shutter speed and then took a photo at each of my ISO settings. As you can see below the lower the ISO setting the darker the photo. At 800 the photo looks too bright - and at 1600 its over exposed. You can see the grain starting to appear at ISO 400.

• Shutter speed: 1/200
• Aperture: F5.6

ISO 100

ISO 200

ISO 400

ISO 800

ISO 1600

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