<Li> Grism, a dispersive prism with a diffraction grating on its surface </Li> <P> Reflective prisms are used to reflect light, in order to flip, invert, rotate, deviate or displace the light beam . They are typically used to erect the image in binoculars or single - lens reflex cameras--without the prisms the image would be upside down for the user . Many reflective prisms use total internal reflection to achieve high reflectivity . </P> <P> The most common reflective prisms are: </P> <Ul> <Li> Porro prism </Li> <Li> Porro--Abbe prism </Li> <Li> Amici roof prism </Li> <Li> Pentaprism and roof pentaprism </Li> <Li> Abbe--Koenig prism </Li> <Li> Schmidt--Pechan prism </Li> <Li> Bauernfeind prism </Li> <Li> Dove prism </Li> <Li> Retroreflector prism </Li> </Ul>

Why are the refracting angles of the two prisms made so small