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Calcium offers two strong absorption lines at 393.3nm and at 396.9nm, known as the K and H lines. Traditionally, university research has employed the Calcium K line for studies of Calcium on the Sun. These studies have been instrumental in determining depth of the solar atmosphere. Researchers have previously avoided the H line for academic research, as it is very close to the Hydrogen Epsilon line. For purposes of clarity in isolating Calcium, and because imaging sensors offer similar sensitivity to the K as the H lines of Calcium, the K has to date been the target of choice in Calcium filters.
However, as the visual spectrum ends at approximately 400nm, the further we venture below this wavelength, the more difficult it is for observers to visually see the image. The H line for visual observations, is much closer to the visual spectrum and easier to see in high contrast violet color.
DayStar offers Calcium H ( 396.9nm ) and Calcium K-line (393.37nm ) filtering systems.