H-alpha filters are essential for imaging nebulae and other objects which are rich in ionized hydrogen. At 656.3nm, a narrow-band emission filter is required to separate H-alpha from the SII doublet (671.6nm and 673.1nm).

All transmission and blocking (OD) data are actual, measured spectra of representative production lots. Spectra varies slightly from lot to lot. Optical density values in excess of 6 may appear noisy because such evaluations push the resolution limit of low light level measurements.