The term 'PART OF A CAMERA LENS' can be summarized by the 4-letter solution 'IRIS'. An IRIS is a diaphragm in a camera lens that can be adjusted to control the amount of light entering the lens. It is made up of several overlapping metal blades that can be opened or closed to create a larger or smaller hole, respectively. The size of the hole determines the amount of light that passes through the lens and onto the film or digital sensor.