Along with the shutter, the iris is the principal component in the camcorder's exposure control system. The camcorder's CCD forms a good image only when exactly the right amount of light enters the camcorder.
Video is shot in a wide range of light levels, from low-lit interiors to bright outdoors.
To accommodate this range as the light grows brighter or dimmer, the lens' iris diaphragm closes or opens, so that the amount of light reaching the camcorder chip is always at a level that guarantees proper exposure. In many consumer camcorders, the iris is controlled automatically. In professional camcorders, the iris can be adjusted manually. On many semi-pro camcorders, like Canon's miniDV XL1, the iris is controlled by a knob on the camera body. When set to this position, the camcorder lens and metering system determines the best exposure for a given scene.