Donut for 6” Ellipsoidal, Source Four Zoom

Donuts are used in the color frame slot of an ellipsoidal reflector spotlight to sharpen gobo projections. Similar to the way the human eye sharpens focus when it squints, a donut reduces the aperture and sharpens the output of the fixture. There is some reduction in brightness to achieve this increase in sharpness but this is often a tradeoff that designers are willing to make.