What Is Infra-Red and How Is It Used When Taking Photographs?

The term ‘infra-red’ refers to a frequency of light invisible to the human eye. Infra-red gets it’s name from its position in the light spectrum, between the red edge of the visible spectrum at 700 nanometers and 1mm. Infra-red light can be used to control photographic equipment, a beam of infra-red light can for example be used to trigger an off camera flash unit. Infra-red light is also used in AF assist illuminates found on flash units; a grid of infra-red light is projected over a subject which helps a contrast detect auto focus system achieve accurate focus in low light conditions.