A beauty dish is simply a shallow parabolic disk that attaches to a light source. There is a plate covering the flash head – this causes the light to reflect back into and out to the sides of the main dish. Most of the light is aimed forward at the model because of the size and curvature of the dish.
When used up close, the beauty dish provides a very focused light source without a hot spot in the middle. It delivers a semi-hard light – softer than an on-camera flash or strobe unit, but harder than a softbox. The beauty dish provides a concentrated light source where the center is the brightest and the light gently falls off at the edges.
The value of the beauty dish is that it sculpts facial features and creates beautiful shadows and catch lights.
This sculpting and defining that a beauty dish does so well is why their use has become so popular in sports portrait photography: the beauty dish accentuates muscles and textures and gives a dramatic and dimensional look to the photograph.