Understanding ISO takes patience, but it is the key to good photography. ISO stands for International Standards Organization, the standardized industry scale for measuring light. In Digital Photography, ISO measures the sensitivity of your camera’s image sensor. In this free video, world renowned outdoor photographer Ian Plant gives you guidance on understanding ISO. As he explains, the lower the ISO number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds, but the images will suffer from digital noise and slightly degrade the quality. If you are in a shooting situation where the light is changing fast such as sports or wildlife, you might want to use your camera’s auto ISO setting.
“Changing ISO changes camera sensitivity” is a common myth. There is no way to change detector sensitivity after the detector array is made. What changing ISO does is apply a variable gain factor to boost the signal. This gain factor obviously makes everything brighter which is why we increase ISO to higher levels in dark scenes. Applying the gain of course also boosts the noise levels so we have to watch out for that.