Beginners Guide: Understanding ISO

ISO is a measure of how sensitive your camera’s sensor (CCD) is to light. The higher the ISO number the more sensitive the sensor is, and therefore the lower the amount of light needed to make an acceptable picture.

Using a higher ISO setting on your camera will allow you to take pictures in lower light. In this way, you can take pictures in lower light without needing long exposures, which would otherwise result in camera shake.

There are two reasons for having the option to change the ISO setting on your digital camera:

1. Versatility

High sensitivity means you need very little light to get the right exposure for your picture. This means you can adopt a range of creative techniques, such as shallow depth of field by using a very wide aperture, or using long exposures to capture motion or increase the effect of blur.

2. Image quality

Digital camera sensors (CCDs) are not very sensitive to light. Most have an optimum ISO setting of ISO 100 or even less. The higher ISO setting is achieved through amplification of the digital signal after the picture has been taken. Consequently, the more you amplify the signal the more noise you get in the final image. This also means the camera’s processor has to use Noise Reduction software to smooth things out. Together noise and noise reduction have a detrimental effect on the image quality (sharpness and colour) as ISO increases.

Using ISO

The default setting on most cameras is auto ISO, where the camera sets the ISO according to the brightness of the scene. Low ISO settings (which offer the very best quality) are used wherever possible, with the sensitivity only increasing where there would otherwise be a risk of camera shake. This is fine for most everyday ‘point and shoot’ photography. You can, however, change the ISO setting manually, and it’s worth getting to grips with this so you, rather than the camera, can make the decision.

ISO 50-100

Use for bright days when you want the best possible quality. Unless you’re shooting with a very long lens you won’t need anything higher in fine weather. You can also use a low ISO setting at night when you want a long exposure (such as when capturing the blur of car headlight trails or shooting fireworks). In such cases you’ll need a tripod to avoid camera shake.

ISO 100-400

Ideal outdoors on overcast days or when using a long lens in bright weather. ISO 200 is often the highest setting you can use without risking noise in your image.

ISO 400-800

For shooting in low light, with a very long zoom or when trying to freeze fast action. ISO 400 is when noise first starts to become a problem, but it’s usually preferable to have a bit of noise than the blur of camera shake

ISO 800-1600

For shooting handheld at night, indoors without flash and in any situation where a lower ISO would cause blur through camera shake or subject motion. Noise is unavoidable at ISO 800 and higher (and most cameras don’t even offer the option).

ISO 1600-3200

Higher ISO settings can also be used to extend the range of your on-camera flash, and to allow even more flexibility in low light (by turning off the flash entirely).

Quick Tips:

• Use a low ISO when taking pictures in good light. This will result in better quality images.
• If you are taking pictures in low light or indoors, you can use a high ISO setting.
• To freeze action or movement, use a high ISO setting. This allows you to use faster shutter speeds.

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