iris (irising)

Iris, or Ising, is an early cinematographic technique or wipe effect, in the form of an expanding or diminishing circle (known as "iris-out" or "iris-in"), in which a part of the screen is blacked out so that only a portion of the image can be seen by the viewer. Usually the lens aperture is circular or oval-shaped and is often expanded or contracted as the film rolls, often as a transition from one scene to the next. This particular type of camera movement is also known as "iris wipe," "circle-in," or "circle-out," similar to the opening or closing of the human eye's iris. Also refers to the adjustable opening (or diaphragm) in the lens that allows light to pass through. The measurement for the iris opening is "f-stop."