A specialised astronomical telescope substantially free from instrumentally scattered light, used to observe the solar corona, the faint atmosphere surrounding the Sun. Coronagraphs can record the emission component of the corona (spectral lines emitted by high-temperature ions surrounding the Sun) and the white-light component (solar photospheric light scattered by free electrons surrounding the Sun) routinely from high mountain sites under clear sky conditions. The emission and white-light components are typically only a few millionths the brightness of the Sun itself. Hence, the corona is difficult to observe unless the direct solar light is completely rejected, and unless instrumentally diffracted and scattered light that reaches the final image plane of the coronagraph is small relative to the coronal light.