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Astronomik
Astronomik 1.25"/2" Narrowband Emission Line H-Alpha-CCD Filters w/ 12nm FWHM & MFR Coating (ASK-HALPHA-12NM-CCD)
from $209.95
Due to the combination of the narrow bandwidth of 12nm and the high transmission of typically 96% the filter gives you an contrast boost, as all unwanted light from other wavelengths than 656nm is blocked...