Current narrow-band optical filters for professional solar astronomy applications are primarily based on Lyot filters.1 However, the Lyot filter is severely limited in operation at UV wavelengths because of the lack of suitable UV hightransmission polarizers. In addition, the Lyot filter is comprised of over 50 elements ~over 30 cm long and weighing several kilograms! that require precise alignment and temperature stabilization for all of the elements.
Elijah E. Cocks,
F. Hadley Cocks,
"Dark-lens diffracting telescope: novel concept for direct extrasolar planet imaging," Optical Engineering 36(10), (1 October 1997). http://dx.doi.org/10.1117/1.601312