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Lee,
All Ha solar telescopes work on the same principle:
An ERF (Energy Rejection Filter) to reduce the total energy into the system - Usually at least a red filter. The better ERF's (Baader D-ERF etc) are actually broadband Ha filters which suppress most of the UV, Visible and IR wavelengths.
The Frabry-Perot etalon - a very expensive interference filter ( two pieces of 1/100 wave reflective plates very close together) which produces a "comb" of light - each "tooth" is usually 0.7A wide and about 10A apart. This "comb" covers the whole spectrum.
By slightly tilting the etalon (or in the case of the Lunt pressure tuned system, the density of the air in the filter) the mid wavelength can be "moved" +/-2A -this allows the Doppler shift to be seen/ recorded.
To isolate the Ha wavelength a blocking (BF), or sort filter is used. This has a bandwidth of around 8A and is tuned to allow only the "tooth" at Ha wavelength to get through.
The ERF/ etalon/ BF are mandatory components. You can't observe or image in solar Ha without them all being in place.
Hope this helps.
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