As the name indicates, the light path through the prisms forms a shape similar to a house roof. Which is how they became 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.