From AMS Glossary
An instrument for photographing the corona and prominences of the sun at times other than at solar eclipse.
An occulting disk is used to block out the image of the body of the sun in the focal plane of the objective lens. The light of the corona passes the occulting disk and is focused on a photographic film. Great care must be taken to avoid light scattered from the atmosphere and the lenses, and from reflections in the tube of the instrument. The coronagraph is used with a narrowband polarizing filter or with a spectroscope.