Mechanical Iris

grabcad

The subject at hand is referred to as a Mechanical Iris, which likely pertains to an optical device that adjusts the amount of light entering a camera or projector lens by varying the size of its aperture. It's called 'mechanical' because it operates with mechanical parts rather than electronically. This type of iris mechanism is typically found in older cameras and projectors, but can still be seen in some modern devices for specific purposes.