ZWO narrowband filters enhance the contrast of emission and planetary nebulae. These peculiar nebulae emit light only in specific wavelengths (H𝛼; OIII ; SII) and the narrowband filters have the property to reject all light outside these bands.
The passing band or "window" of these filters is 7nm wide. Considering that the visible light spectrum spaces between 380nm and 740nm, a 7nm filter would block 98% of the unwanted light. As a result, the signal to noise ratio between the light of the nebulae (signal) and the noise (moonlight, light pollution, airglow) is highly increased.
Nebulae have a strong emission on the band of the hydrogen (H𝛼), oxygen (O III) and the sulfur (S II). Having 3 wavelengths in 3 different areas of the visible spectrum, it is possible to recreate a false colour image of a nebula.