The SIICCD 7nm Photographic Extra Narrowband Filter is designed for nebula observation. Allowing 7nm bandwidth of light centered on a wavelength of 672nm through. Which adds in reducing the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high- and low-pressure sodium vapor lights. Also including the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).