As the name indicates, the light path through the prisms forms a shape similar to a house roof. Which is how they came to be called "roof prism". In roof prisms the light is deflected by reflective coatings. At least one surface must be coated, either with a silver or dielectric coating. The light ray is reflected in five places, until it reaches the eyepiece. It is considerably more complex to manufacture a good roof prism system, since the light loss on the reflective surfaces must be kept as low as possible. Sometimes so-called Abbe-König prisms are used, here the surfaces do not need to be coated.