ETC DN7.5-2650-5 Donut, 7.5-Inch / 190-Millimeter and 3.5-Inch / 89-Millimeter Aperture (For XDLT 26 And 50) - Silver
Donuts help sharpen gobo projections by reducing the diameter of the output lenses. Similar to squinting an eye, this reduction helps improve clarity of the projected gobo, however a reduction in brightness is a side effect.