We describe the properties of the Zeiss Universal Birefringent Filter and its optical and electronic interface with the Sacramento Peak Observatory'’ vacuum telescope. The instrument permits observations of solar intensities, velocities, and/or magnetic fields in rapid succession in any Fraunhofer line in the 410–700-nm wavelength region with high spectral (0.004–0.013 nm) and high spatial (~1/3 sec of arc) resolution.
Jacques M. Beckers, Larry Dickson, and Randy S. Joyce, "Observing the sun with a fully tunable Lyot-Ohman filter," Appl. Opt. 14, 2061-2066 (1975)