The spectroheliograph captures a photographic image of the Sun at a single wavelength of light. The wavelength chosen usually coincides with a spectral wavelength of one of the chemical elements present in the Sun.
George Ellery Hale and Henri-Alexadre Deslandres developed I independently in 1890 and was further refined in 1932 by Robert R. McMath to take motion pictures.
It operates by using a prism together with a narrow slit that passes a single wavelength. The light focuses on a photographic medium and the slit is moved across the disk of the sun to form a complete image. Now it is possible to make a filter that transmits a narrow band of wavelengths which produces a similar image.