Iris

The lens's adjustable pupil, opening and closing around the light. Also the old transition: a circle closing on the world.

The iris is aperture as mechanism: overlapping blades forming a near-circle whose size is the f-stop made physical. Its blade count and shape sign the image, bokeh takes the iris's geometry, and cinema lenses pay for rounder pupils precisely so out-of-focus light stays gentle.

The word's second life is the iris transition, silent film's closing circle, the world shrinking to one detail and going dark. It survives as homage and in animation, and its logic, ending by narrowing attention, outlived its fashion. Every vignette that darkens corners is the iris speaking quietly.