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ISO is one of the pillars of exposure – here’s how it affects your images

ISO (International Standards Organisation) is the standardised scale for measuring light sensitivity. The higher the ISO number, the more sensitive to light the film or sensor is, and the more noise/grain is introduced into an image. This is because film contains countless light-sensitive silver halide crystals. Fine crystals are used in low-speed film (ISO 100) while fatter crystals, visible to the eye as grains, in high-speed film (ISO 1 600) to absorb more light. In digital cameras this is replicated by electrical charge. The higher the ISO the more electric charge runs through the sensor. Noise is the by-product of that electrical charge and it degrades image quality and colour. How to use ISO to your benefit A higher ISO means more light is absorbed and a faster shutter speed can be set to get a good exposure. Use it to limit camera shake in low-light situations, or to prevent blur in fast-moving objects.